Refactoring the code a bit here to make the `Rocket` instance available
to the integration tests. To do this, we have to convert to a library
crate (`lib.rs`) with an executable entry point (`main.rs`). This
allows the tests, which are separate crates, to import types and
functions from the library.
Besides splitting the `rocket` function into two parts (one in `lib.rs`
that creates the `Rocket<Build>` and another in `main.rs` that becomes
the process entry point), I have reworked the initialization process to
make better use of Rocket's "fairings" feature. We don't want to call
`process::exit()` in a test, so if there is a problem reading the
configuration or initializing the context, we need to report it to
Rocket instead.
We'll use a JWT in the `Authorization` request header to identify the
user saving a page. The token will need to be set in the _authorization
token_ field in the SingleFile configuration so it will be included when
uploading.
